FWIW I had the same exact problem at the same exact screen. The fix is simple but is anything but intuitive, especially because there's nothing on this screen that indicates what you are supposed to do.
You arrive at this screen if you have collected more weapons than you can carry. Near the top of the screen you'll see a fraction where the numerator is the number of weapons you've collected, and the denominator is the number of weapons you can carry. In my case it was "25/20".
Numerator minus denominator. In my case, it was 25 - 20 = 5. I was five items "too heavy" and so I needed to get rid of (sell) five items.
Select the weapons you wish to "sell" by hovering over them and hitting the "A" button. The weapon should turn red. I would pick your weakest weapons.
Once you have selected the number of weapons you need to be at or below your carrying capacity, finally, a Confirm button/option will appear at the bottom of the screen. Scroll down to it and select it, and boom -- you're past this screen.
This is screen is a hot mess that was really frustrating for me.